Ecologists want to know how different populations interact with each other.
All of the populations within the community and the associated abiotic variables are included.
Chemical cycling and energy flow are important parts of an ecology.
There are rarely rigid boundaries.
An ecotone is a transition zone that has a mixture of organisms from adjacent ecosystems.
The zones of the Earth's soil, water, and air are encompassed.
Modern ecology is more than just descriptive.
It develops models and hypotheses that can be tested.
The goal of modern ecology is to develop models that explain and predict the distribution and potential abundance of organisms.
Ecologists try to determine which factors have been selected for the mix of plants and animals in a tropical rain forest at one latitude compared to a desert at another.
Modern ecology has many application possibilities, including the proper management of plants and wildlife, the identification of and efficient use of renewable and nonrenewable resources, the preservation of habitats and natural cycles, the maintenance of food resources, and the ability to predict.
Understand how the proportion of individuals at different reproductive stages affects a population's age distribution.
The population density in the United States is about 90 people per square mile.
Population density figures can make it seem like individuals are distributed uniformly.
In the United States, most people live in cities where the number of people per unit area is higher than in the country.
Even within a city, more people live in certain neighborhoods than in others, and this can change over time.
Population density can lead to inaccurate results in ecological models.
Where populations live can be affected by the availability of resources.
Resources are components of an environment that support living organisms.
In high latitudes and mountainous regions, the timberline is the limit of tree growth.
Trees can't grow above the high timberline because of low temperatures and frozen water.
The distribution of organisms can be influenced by biotic factors.
The red kangaroo does not live outside of arid inland areas in Australia because it is adapted to feeding on the grasses there.
Patterns of distribution can be characterized.
If you were to consider the distribution of a species across its full range, what would it look like?
A range is the portion of the globe where the species can be found.
A clumped distribution would be expected on that scale.
Red kangaroos and catfish live in warm river water near the coast, which is suitable for their adaptation.
The availability of resources affects which pattern of distribution is exhibited for a particular population.
A study of the distribution of hard clams in a bay on the south shore of Long Island, New York, showed that clam abundance is associated with shell content.
In areas with low clam populations investigators hope to increase the density and number of clams.
Distribution patterns don't need to be constant.
As the desert shrubs matured, the distribution changed from random to a uniform pattern.
Competition for belowground resources caused the distribution pattern to change over time.
Small desert shrubs are clumped.
Medium shrubs are distributed randomly.
The shrubs are uniformly distributed.
Territoriality is one of the behavioral characteristics of golden eagles.
cedar trees tend to be clumped near the parent plant because seeds are not widely dispersed.
The growth rate is determined by the number of individuals born each year and the number of individuals that die each year.
Populations grow when there are more births than deaths.
The rate of natural increase for a population is called the highest possible rate.
A population's maximum growth rate under ideal conditions is influenced by the number of offspring produced in each reproductive event.
Population growth patterns assume that populations are made up of the same people.
People in a population are in different stages of their lives.
Some investigators study population dynamics and build life tables that show how many people are still alive after a certain period of time.
For a bluegrass cohort, Table 44.1 is a life table.
The cohort contains many people.
The mortality rate after 3 months is 0.143 per capita.
722 people are still alive after 3 months, which is another way to say the same thing.
A survivorship curve is produced if we plot the number surviving at each age.
The results of investigations like this have shown that each species is able to live past the halfway point of the life span.
Large mammals and humans can be found in more developed countries.
The type III curve is typical of a population in which most people die young.
This curve occurs in many plants and animals.
Death is unrelated to age in many songbirds and small mammals.
The number of people who are still alive is shown by the survivorship curves.
The type I and type II curves are represented by the survivorship curve.
The survivorship curve for lizards is a type II curve.
There is a curve for mosquitoes.
Page 832 does not fit the survivorship curves of natural populations.
In a bluegrass cohort, most individuals survive until 6-9 months, and then the chances of surviving diminish at an increasing rate.
A mosquito cohort has a type III curve, while a lizard cohort has a type II curve.
It is possible to learn a lot about the life history of a species by studying its life table and survivorship curve.
Natural selection would favor individuals with more offspring in a population with a type III survivorship curve.
Natural selection favors those that produced more offspring because death comes early for most members.
Studying life tables can provide other types of information.
As plants mature and seed production drops off, we can see that per-capita seed production increases.
Several generations may be alive at the same time when individuals in a population reproduce repeatedly.
The population has three major age groups: prereproductive, reproductive, and postreproductive.
The proportion of the population that falls into each age group is different.
There are age structure diagrams for populations that are increasing or decreasing.
The left half of the diagram is for males and the right half is for females.
The prereproductive group is the largest of the three groups if the birthrate is higher than the death rate.
This shows a pyramid-shaped diagram.
If the growth for that year were matched by the deaths for that year, the population would continue to grow.
More people would be entering than leaving the reproductive group.
As the size of the reproductive group equals the size of the prereproductive group, a bellshaped diagram results.
Because of mortality, the postreproductive group is still the smallest.
The reproductive group becomes smaller if the birthrate falls below the death rate.
The postreproductive group is the largest in the age structure diagram.
The past and future history of a population are reflected in the age distribution.